Why do you think it's only "a day." Also, you are forever introducing a dependency in your build chain, codebase, and executable. EVERY 3rd party dependency should be audited as such (performance, security, usability, etc). Boost is no exception, but for the amount of things it comes with (often), and the strain on the compiler requirements it produces, it is typically included as a last resort.
I should mention, people who talk without much context are a curious bunch too.
Yes there is always a balance of concerns. Build management with 3rd party deps is not trivial but its part of the lifecycle. In my experience boost integration really is "a day" on windows (including stashing the .libs as their own repo and reproducing a fresh 'git clone' build), and 10 minutes on a platform that you can use the package manager to obtain it. You can always excise it from a project later if you dont abuse 'using' statements. FWIW, I only really use variant and ASIO.
If you were adding boost to a project just to do some weird spirit/preprocessor hacks, I'd be wary. But if you told me you were going to write yet another cross platform ASIO wrapper because you couldn't figure out how to compile boost I'd be even more concerned.
I should mention, people who talk without much context are a curious bunch too.